Algae resistant roofing granules with controlled algaecide leaching rates, algae resistant shingles and process for producing same

ABSTRACT

Algae-resistant roofing shingles are prepared with granules are formed by coating mineral particles with a clay-silicate binder including a metal oxide algaecide and small organic particles. When the particles are heated to cure the binder, the organic particles pyrolyse to form pores in the coating. Release of the algaecide is controlled by the structure of the granules.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 12/610,782, filed Nov. 12, 2009, which was a division of U.S.patent application Ser. No. 10/600,847, filed Jun. 20, 2003, now U.S.Pat. No. 7,687,106, issued Mar. 30, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to asphalt roofing shingles, andprotective granules for such shingles, and processes for makings suchgranules and shingles.

2. Brief Description of the Prior Art

Pigment-coated mineral rocks are commonly used as color granules inroofing applications to provide aesthetic as well as protectivefunctions to the asphalt shingles. Dark blotches or streaks sometimesappear on the surfaces of asphalt shingles, especially in warmer humidclimates, as a result of the growth of algae and other microorganisms.The predominant species responsible is Gloeocapsa magma, a blue greenalgae. Eventually, severe discoloration of the entire roof can occur.

Various methods have been used in an attempt to remedy the roofingdiscoloration. For example, topical treatments with organic algaecideshave been used. However, such topical treatments are usually effectiveonly for short term, typically one to two years. Another approach is toadd algaecidal metal oxides to the color granule coatings. This approachis likely to provide longer protection, for example, as long as tenyears.

Companies, including Minnesota Mining and Manufacturing (3M) and GAFMaterials Corporation/ISP Mineral Products Inc., have commercializedseveral algaecide granules that are effective in inhibiting algaegrowth.

A common method used to prepare algae-resistant (AR) roofing granulesgenerally involves two major steps. In the first step, metal oxides suchas cuprous oxide and zinc oxide are added to a clay and alkali metalsilicate mixture that in turn is used to coat crushed mineral rocks. Themixture is rendered insoluble on the rock surfaces by firing at hightemperatures, such as about 500° C., to provide a ceramic coating. Inthe second step, the oxides covered rocks are coated with various colorpigments to form colored algae-resistant roofing granules. Thealgae-resistant granules, alone, or in a mixture with conventionalgranules, are then used in the manufacture of asphalt shingles usingconventional techniques. The presence of the algae-resistant granulesconfers algae-resistance on the shingles.

Roofing granules typically comprise crushed and screened mineralmaterials, which are subsequently coated with a binder containing one ormore coloring pigments, such as suitable metal oxides. The binder can bea soluble alkaline silicate that is subsequently insolubilized by heator by chemical reaction, such as by reaction between an acidic materialand the alkaline silicate, resulting in an insoluble colored coating onthe mineral particles.

U.S. Pat. No. 3,507,676 discloses roofing granules containing zinc, zincoxide, or zinc sulfide, as an algaecide and fungicide.

Algae-resistant shingles are disclosed, for example, in U.S. Pat. No.5,356,664 assigned to Minnesota Mining and Manufacturing Co., whichdiscloses the use of a blend of algae-resistant granules andnon-algae-resistant granules. The algae-resistant granules have an innerceramic coating comprising cuprous oxide and an outer seal coatinginitially devoid of copper.

There is a continuing need for algae-resistant roofing products havingalgaecide leaching rates that can be controlled so that the roofingproducts can be tailored for specific local conditions.

SUMMARY OF THE INVENTION

The present invention provides algae-resistant roofing granules havingalgaecide leaching rates that can be easily controlled, and asphaltshingle roofing products incorporating such algae-resistant roofinggranules.

The present invention employs mineral particles to form algae-resistantroofing granules. In contrast to prior processes for formingalgae-resistant granules, which typically rely only upon porositydeveloped during cure of a ceramic binder, typically a sodiumsilicate/aluminosilicate binder cured chemically or thermally, theprocess of the present invention employs void-forming additives tocontribute to porosity and thus control the leach rate of algaecidalmaterial from the roofing granules.

This invention thus provides a process for preparing algae-resistantroofing granules having algaecide leaching rates that can be controlledand modified at will.

The present process for producing algae-resistant roofing granulescomprises providing inert base particles and forming first intermediateparticles by coating the inert base particles with a first mixture toform a first layer on the inert base particles. The inert particles canbe, for example, crushed rock. The first mixture includes at least onealgaecidal material, a void-forming material, and preferably, a binder.The binder can include an aluminosilicate material such as clay, and asoluble silicate, such as aqueous sodium silicate. The void-formingmaterial preferably releases gaseous material above 90° C., and has anaverage particle size no larger than about 2 mm. The void-formingmaterial can be decomposable into gaseous by-products at temperaturesabove about 150° C. In the alternative, the void forming material cansimply release moisture as a gaseous material to form the desired voids.

The present process preferably further comprises forming secondintermediate particles by coating the first intermediate particles witha second mixture including a coloring material. The second mixture caninclude a binder, such as a binder having the same composition as thefirst mixture. The second mixture can also optionally comprise avoid-forming material. Further, the second mixture can optionallyinclude at least one algaecidal material.

The process requires heating the first and/or second intermediateparticles, preferably above the temperature at which the gaseousmaterial is released, to release the gaseous material and form pores inthe first layer to produce the roofing granules.

Metal oxides are preferred as algaecidal materials due to theirfavorable cost and performance. The at least one algaecidal material ispreferably selected from the group consisting of copper compounds andzinc compounds. For example, cuprous oxide and/or zinc oxide can beemployed. In one presently preferred embodiment of the presentinvention, both cuprous oxide and zinc oxide are used, and the cuprousoxide comprises about 2 to 6 percent of the algae-resistant granules,and the zinc oxide comprises about 0.1 to 2 percent by weight of thealgae-resistant granules.

The void-forming material can be an organic or inorganic compound, andcan be either water soluble or insoluble. Examples of decomposablevoid-forming materials include sugar, crushed nuts (such as walnutshells), crushed corn and grains, carbon or graphite balls, syntheticand natural polymers, organic fibers, flame retardants and hydratedcompounds.

The void-forming material preferably comprises a substance selected fromthe group consisting of ground walnut shells, sugar, and carbon black.In one presently preferred embodiment of the present invention, thevoid-forming material comprises about 0.5 to 5 percent by weight of thealgae-resistant granules.

The void-forming material can release gaseous material, or decompose orevaporate at elevated temperature, leaving behind hollow openings thatprovide additional avenues for the metal ions to leach out easily.

The present invention also provides a process for producingalgae-resistant roofing shingles, as well as the shingles themselves.This process comprises producing algae-resistant roofing granules usingthe process of this invention, and adhering the granules to a shinglestock material.

The algaecidal material concentration preferably is from about 0.1% toabout 10% of the total granule weight, and that of the void-formingmaterial is preferably from about 0.05 to about 5%. Various combinationsof the levels and types of the void-forming materials used in theformulations can provide different amounts of algaecidal materialleaching out from the granules.

The algae-resistant granules prepared according to the process of thepresent invention can be employed in the manufacture of algae-resistantroofing products, such as algae-resistant asphalt shingles. Thealgae-resistant granules of the present invention can be mixed withconventional roofing granules, and the granule mixture can be embeddedin the surface of bituminous roofing products using conventionalmethods. Alternatively, the algae-resistant granules of the presentinvention can be substituted for conventional roofing granules inmanufacture of bituminous roofing products, such as asphalt roofingshingles, to provide those roofing products with algae-resistance.

In one embodiment, the present invention provides a process forpreparing AR roofing granules having a controllable algaecide-leachingrate.

In another embodiment, the present invention provides a process forpreparing roofing shingles having algae-resistance that can becustomized to the specific geographic region in which the shingles areintended to be used.

The present invention preferably provides algae-resistant roofinggranules having controllable levels of algaecide release.

The present invention also preferably provides algae resistant asphaltshingles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the effect of various types ofvoid-forming material on the concentrations of copper ions leached outfrom granules prepared according to the present invention (after 8 daysimmersion in warm water of 60° C.). The values above the bars depict thecopper concentrations in ppm.

FIG. 2 is a graph illustrating the effect of various types ofvoid-forming material on the concentrations of zinc ions leached outfrom granules prepared according to the present invention (after 8 daysimmersion in warm water of 60° C.). The values above the bars depict thecopper concentrations in ppm.

FIG. 3 is a graph illustrating the effect of varying the amount ofvoid-forming material on the concentrations of zinc ions leached outfrom granules prepared according to the present invention (after 8 daysimmersion in warm water of 60° C.). The values above the bars depict thecopper concentrations in ppm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The inert base particles employed in the process of the presentinvention are preferably chemically inert materials, such as inertmineral particles. The mineral particles, which can be produced by aseries of quarrying, crushing, and screening operations, are generallyintermediate between sand and gravel in size (that is, between about 8US mesh and 40 US mesh), and preferably have an average particle size offrom about 0.2 mm to about 3 mm, and more preferable from about 0.4 mmto about 2.4 mm.

In particular, suitably sized particles of naturally occurring materialssuch as talc, slag, granite, silica sand, greenstone, andesite,porphyry, marble, syenite, rhyolite, diabase, greystone, quartz, slate,trap rock, basalt, and marine shells can be used, as well as recycledmanufactured materials such as crushed bricks, concrete, porcelain, fireclay, and the like.

The process of the present invention for producing algae-resistantroofing granules comprises providing inert base particles, and formingfirst intermediate particles by coating the inert base particles with afirst mixture to form a first layer on the inert base particles. Thisfirst mixture includes at least one algaecidal material, at least onevoid-forming material, and, preferably, a binder.

The void-forming material can be an organic material or inorganiccompound. Preferably, the void-forming material is selected so that itreleases gaseous material, such as by decomposing into gaseous products,at suitably elevated temperatures. The void-forming material preferablyreleases gaseous material at a temperature that is greater than 90degrees C. The void-forming material may, for example, release boundwater, or water of hydration, at the elevated temperature. In thealternative, the void-forming material may itself decompose at anelevated temperature, preferably at a temperature above about 150degrees C. Examples of void-forming materials include sugar, sugar-basedproducts such as candy “sprinkles,” crushed nuts (such as walnutshells), crushed corn and grains, carbon or graphite balls, syntheticand natural polymers, organic fibers, flame-retardants, and hydratedcompounds. The void-forming material can be either water-soluble orwater-insoluble. Preferably, the void-forming material comprises atleast 0.1 percent by weight of the algae-resistant granules. Preferably,the void-forming material has an average particle size no larger thanabout 2 mm. The void-forming material preferably has an average particlesize from about 100 μm to about 400 μm. Mixtures of void-formingmaterials can also be used, as well as mixture of water-soluble andwater-insoluble void-forming material. The proportions of mixtures ofvoid-forming materials can be tailored to achieve desired leachingcharacteristics for the resulting algae-resistant particles. Thevoid-forming material preferably comprises a substance selected from thegroup consisting of ground walnut shells, sugar, and carbon black. Inone presently preferred embodiment of the present invention, thevoid-forming material comprises about 1.4 percent by weight of thealgae-resistant granules.

The at least one algaecide is preferably selected from the groupconsisting of copper materials, zinc materials, and mixtures thereof.For example, cuprous oxide and/or zinc oxide, or a mixture thereof, canbe used. The copper materials that can be used in the process of thepresent invention include cuprous oxide, cupric acetate, cupricchloride, cupric nitrate, cupric oxide, cupric sulfate, cupric sulfide,cupric stearate, cupric cyanide, cuprous cyanide, cuprous stannate,cuprous thiocyanate, cupric silicate, cuprous chloride, cupric iodide,cupric bromide, cupric carbonate, cupric fluoroborate, and mixturesthereof. The zinc materials can include zinc oxide, such as Frenchprocess zinc oxide, zinc sulfide, zinc borate, zinc sulfate, zincpyrithione, zinc ricinoleate, zinc stearate, zinc chromate, and mixturesthereof. In one embodiment, the at least one algaecide preferablycomprises cuprous oxide, and it is preferred that the cuprous oxidecomprises at least 2 percent of the algae resistant granules. In anotherembodiment, the at least one algaecide preferably comprises zinc oxide,and it is preferred that the zinc oxide comprises at least 0.1 percentby weight of the algae-resistant granules. When a mixed algaecide isemployed, the at least one algaecide preferably comprises a mixture ofcuprous oxide and zinc oxide.

The binder employed in the process of the present invention to form thefirst intermediate particles is preferably formed from a mixture of analkali metal silicate, such as aqueous sodium silicate, and heatreactive aluminosilicate material, such as clay, preferably, kaolin. Theproportion of alkali metal silicate to heat-reactive aluminosilicatematerial is preferably from about 3:1 to about 1:3 parts by weightalkali metal silicate to parts by weight heat-reactive aluminosilicatematerial, more preferably about 2:1 to about 0.8:1 parts by weightalkali metal silicate to parts by weight heat-reactive aluminosilicatematerial.

When the algae-resistant granules are fired at an elevated temperature,such as at least about 200 degrees C., and preferably about 250 to 500degrees C., the clay reacts with and neutralizes the alkali metalsilicate, thereby insolubilizing the binder. The binder resulting fromthis clay-silicate process, believed to be a sodium aluminum silicate,is porous, such as disclosed in U.S. Pat. No. 2,379,358 (incorporatedherein by reference). Alternatively, the porosity of the insolubilizedbinder can be decreased by including an oxygen containing boron compoundsuch as borax in the binder mixture, and firing the granules at a lowertemperature, for example, about 250 degree C. to 400 degrees C., such asdisclosed in U.S. Pat. No. 3,255,031 (incorporated herein by reference).

Examples of clays that can be employed in the process of the presentinvention include kaolin, other aluminosilicate clays, Dover clay,bentonite clay, etc. The binder employed in the present invention caninclude an alkali metal silicate such as an aqueous sodium silicatesolution, for example, an aqueous sodium silicate solution having atotal solids content of from about 38 percent by weight to about 42percent by weight, and having a ratio of Na₂O to SiO₂ of from about 1:2to about 1:3.25.

In the initial step of the process of the present invention, firstintermediate particles are formed by coating the inert base particleswith a mixture to form a first layer on those inert base particles.Preferably, the first layer has a thickness of from about 10 μm to about50 μm, more preferably about 30 μm. The first intermediate particles canbe fired as described above to cure the binder, and to release thegaseous material from the at least one void-forming material to form thedesired voids or pores in the first coating. When the void-formingmaterial is an organic compound, the applied heat can pyrolyse thecompound resulting in the desired pores. The algaecidal properties ofthe algae-resistant granules can be tailored by controlling the porosityand distribution of the algaecidal material. Preferably, the granuleshave a pore size in the range of about 0.1 μm to 20 μm.

The present process preferably further comprises forming secondintermediate particles by coating the first intermediate particles witha second mixture including a coloring material to form a second layer.The second mixture can include a binder, such as a binder having thesame composition as the first mixture. The second intermediate particlesare fired to cure the binder. The second mixture can optionally includea void-forming material, so as to increase the porosity of the curedcoating ultimately formed. Further, the second mixture can optionallyinclude at least one algaecidal material, such as cuprous oxide.Preferably, the second layer has a thickness of from about 2 μm to about25 μm, more preferably about 5 μm. Preferably, the second intermediateparticles are formed by coating the first intermediate particles withoutfiring the first intermediate particles to cure the first binder. Thisreduces the energy required to produce the algae-resistant particles ofthe present invention by reducing the number of energy-consuming firingsteps from two to one.

In alternative embodiment of the process of the present invention, theinert base particles are coated with a single mixture including binder,at least one void-forming material, at least one algaecidal material,and at least one colorant, to provide “intermediate” particles. Theintermediate particles are subsequently fired at elevated temperature toboth cure the binder and decompose the at least one void-formingmaterial thus providing the desired voids or pores in the granulecoating.

The algae-resistant roofing granules of the present invention can becolored using conventional coatings pigments. Examples of coatingspigments that can be used include those provided by the Color Divisionof Ferro Corporation, 4150 East 56th St., Cleveland, Ohio 44101, andproduced using high temperature calcinations, including PC-9415 Yellow,PC-9416 Yellow, PC-9158 Autumn Gold, PC-9189 Bright Golden Yellow,v-9186 Iron-Free Chestnut Brown, V-780 Black, V0797 IR Black, V-9248Blue, PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red, V-12600Camouflage Green, V12560 IR Green, V-778 IR Black, and V-799 Black.Further examples of coatings pigments that can be used include whitetitanium dioxide pigments provided by Du Pont de Nemours, P.O. Box 8070,Wilmington, Del. 19880.

The algaecide resistance properties of the algaecide resistant roofinggranules of the present invention are determined by a number of factors,including the porosity of the roofing granules, the nature and amount(s)of the algaecide employed, and the spatial distribution of the algaecidewithin the granules.

The process of the present invention advantageously permits the algaeresistance of the shingles employing the algae-resistant granules to betailored to specific local conditions. For example, in geographic areasencumbered with excessive moisture favoring rapid algae growth, thegranules can be structured to release the relatively high levels ofalgaecide required to effectively inhibit algae growth under theseconditions. Conversely, where algae growth is less favored by localconditions, the granules can be structured to release the lower levelsof algaecide effective under these conditions.

The algae resistance properties of the granule bodies can also be variedthrough control of the porosity conferred by the binder employed. Forexample, the binder porosity can be controlled by adjusting the ratio ofthe aqueous silicate and the aluminosilicate employed.

Combinations of the above-described alternatives for introducingalgaecide into and/or on the granule bodies can also be employed. Byadjusting the amount and selecting the type of algaecide used, and byadjusting the porosity of the granules, a variety of different algaecideleach rates and leaching profiles can be obtained.

The algae-resistant granules prepared according to the process of thepresent invention can be employed in the manufacture of algae-resistantroofing products, such as algae-resistant asphalt shingles, usingconventional roofing production processes. Typically, bituminous roofingproducts are sheet goods that include a non-woven base or scrim formedof a fibrous material, such as a glass fiber scrim. The base is coatedwith one or more layers of a bituminous material such as asphalt toprovide water and weather resistance to the roofing product. One side ofthe roofing product is typically coated with mineral granules to providedurability, reflect heat and solar radiation, and to protect thebituminous binder from environmental degradation. The algae-resistantgranules of the present invention can be mixed with conventional roofinggranules, and the granule mixture can be embedded in the surface of suchbituminous roofing products using conventional methods. Alternatively,the algae-resistant granules of the present invention can be substitutedfor conventional roofing granules in manufacture of bituminous roofingproducts to provide those roofing products with algae-resistance.

Bituminous roofing products are typically manufactured in continuousprocesses in which a continuous substrate sheet of a fibrous materialsuch as a continuous felt sheet or glass fiber mat is immersed in a bathof hot, fluid bituminous coating material so that the bituminousmaterial saturates the substrate sheet and coats at least one side ofthe substrate. The reverse side of the substrate sheet can be coatedwith an anti-stick material such as a suitable mineral powder or a finesand. Roofing granules are then distributed over selected portions ofthe top of the sheet, and the bituminous material serves as an adhesiveto bind the roofing granules to the sheet when the bituminous materialhas cooled. The sheet can then be cut into conventional shingle sizesand shapes (such as one foot by three feet rectangles), slots can be cutin the shingles to provide a plurality of “tabs” for ease ofinstallation, additional bituminous adhesive can be applied in strategiclocations and covered with release paper to provide for securingsuccessive courses of shingles during roof installation, and thefinished shingles can be packaged. More complex methods of shingleconstruction can also be employed, such as building up multiple layersof sheet in selected portions of the shingle to provide an enhancedvisual appearance, or to simulate other types of roofing products.

The bituminous material used in manufacturing roofing products accordingto the present invention is derived from a petroleum-processingby-product such as pitch, “straight-run” bitumen, or “blown” bitumen.The bituminous material can be modified with extender materials such asoils, petroleum extracts, and/or petroleum residues. The bituminousmaterial can include various modifying ingredients such as polymericmaterials, such as SBS (styrene-butadiene-styrene) block copolymers,resins, flame-retardant materials, oils, stabilizing materials,anti-static compounds, and the like. Preferably, the total amount byweight of such modifying ingredients is not more than about 15 percentof the total weight of the bituminous material. The bituminous materialcan also include amorphous polyolefins, up to about 25 percent byweight. Examples of suitable amorphous polyolefins include atacticpolypropylene, ethylene-propylene rubber, etc. Preferably, the amorphouspolyolefins employed have a softening point of from about 130 degrees C.to about 160 degrees C. The bituminous composition can also include asuitable filler, such as calcium carbonate, talc, carbon black, stonedust, or fly ash, preferably in an amount from about 10 percent to 70percent by weight of the bituminous composite material.

The following examples are provided to better disclose and teachprocesses and compositions of the present invention. They are forillustrative purposes only, and it must be acknowledged that minorvariations and changes can be made without materially affecting thespirit and scope of the invention as recited in the claims that follow.

Example 1

1,000 g of crushed and screened rhyolite igneous rock from Wrentham,Mass. having an average particle size of 1 mm are mixed for 2 minutes ina paddle mixer with 40 g of aqueous sodium silicate (40% solids, withNa₂O:SiO₂ ration of 1:3.2) (Occidental Chemical Corporation, Dallas,Tex.), 30 g of Wilkinson brand kaolin clay, 35 g of Chemet brand cuprousoxide (American Chemet Corporation, Deerfield, Ill.) and 1.75 g of Kadoxbrand zinc oxide (Zinc Corporation of America, Monaca, Pa.), and 6.5 gof Regal carbon balls supplied by Cabot Corporation (Boston, Mass.) andhaving a chemical composition of 90% carbon black and an averageparticle size of 25 nm, to form green granules having a particle size ofabout 1 mm. The green granules are then fired in a gas-fired kiln at atemperature of 500 degrees C. for 20 minutes to form algae-resistantgranules according to the present invention.

Example 2

The process of Example 1 is repeated, except that 30 g of table sugar(Domino) having an average particle size of 20 μm is substituted for thecarbon balls.

Example 3

The process of Example 1 is repeated, except that 12 g of candy sugar“sprinkles” (Signature) having an average particle size of 1.2 mm aresubstituted for the carbon balls.

Example 4

The process of Example 1 is repeated, except that 30 g of crushed walnutshells (Composite Materials, Inc.) and having an average particle sizeof 300 μm are substituted for the carbon balls.

Example 5

The process of Example 3 is repeated, except that 30 g of candy sugar“sprinkles” are employed.

Example 6

The process of Example 4 is repeated. 500 g of the granules produced aremixed with a coating mixture for 2 minutes in a paddle mixer, thecoating mixture comprising 16 g of aqueous sodium silicate (40% solids,with Na₂O:SiO₂ ratio of 1:3.2), 10 g of kaolin clay, 6 g of V-780(black) pigment particles (Ferro Corporation) to form coated granules(second intermediate particles) having a particle size of about 1 mm.The coated granules are then fired in a gas-fired kiln at a temperatureof about 500 degrees C. for 20 minutes to form colored, algae-resistantgranules according to the present invention.

Example 7

The process of Example 6 is repeated, except that 3 g of Regal carbonballs are added to the coating mixture to increase the porosity of thefired coating.

Example 8

The process of Example 6 is repeated, except that 7 g of Chemet brandcuprous oxide and 0.35 g of Kadox brand zinc oxide are added to thecoating mixture.

Example 9

The process of Example 6 is repeated, except that twice as much of theChemet brand cuprous oxide was used in the inner coating, that is, 60 gof cuprous oxide for the inner coating, and 10 g of cuprous oxide isadded to the outer coating, so that there is cuprous oxide in both theinner and the outer coatings.

Example 10

The process of Example 4 is repeated, except that 70 g of Chemet brandcuprous oxide, plus 12 g of V-780 Ferro brand black pigment particlesare used to form single-coated, algae-resistant granules.

Comparative Example 1

The process of Example 1 is repeated, except that the carbon balls areomitted.

The effect of varying the type of void-forming material on thealgae-resistance of the algae-resistant granules of the presentinvention was determined. 100 g of algae-resistant granules prepared asdescribed above in Examples 1-4 and Comparative Example 1 were immersedfor 8 days in 100 g of distilled water at 60 degrees C. Theconcentration of copper ion and zinc ion in the leach water was thendetermined by inductively coupled plasma (ICP) emission spectroscopy,and the results are shown in FIGS. 1 and 2. As depicted in FIGS. 1 and2, candy sprinkles result in much higher leaching of copper (22.24 ppm)and zinc (2.14 ppm) ions than other additives do.

The effect of varying the amount of void-forming material on thealgae-resistance of the algae-resistant granules of the presentinvention was also determined. 100 g of algae-resistant granulesprepared as described in Examples 3 and 5 and Comparative Example 1above were immersed for 8 days in 100 g of distilled water at 60 degreesC. The concentration of copper ion and zinc ion in the leach water wasthen determined by ICP emission spectroscopy, and the results are shownin FIG. 3. The results displayed in FIG. 3 show that granules containinga higher level of sugar sprinkles (30 g per kg of granules) leach outmore copper ions than the lower sugar sprinkles or no additive.

A comparison of the leaching rates for one-coat and two-granules wasmade as follows:

10 g of algae-resistant granules prepared as described in Examples 9 and10 were immersed in 10 ml of acetate buffer solution (pH 4.6) at 60° C.for various days. The concentration of cooper ions in the leachedsolution was determined by first reacting the copper ions withdipotassium 2,2′ bicinchoninate to form a colored complex, followed bymeasuring the color intensity of the formed complex at 560 nm using alaboratory spectrophotometer. The results, plotted in FIG. 4, show thatgranules prepared by the one-coated process have higher total leachedamounts of copper ions than the two-coated granules have.

Various modifications can be made in the details of the variousembodiments of the processes, compositions and articles of the presentinvention, all within the scope and spirit of the invention and definedby the appended claims.

1. An algae-resistant roofing product produced by a process comprising producing algae-resistant roofing granules, and adhering the granules to a roofing product stock material, the algae-resistant roofing granules being produced by a process comprising: (a) providing inert base particles; (b) forming first intermediate particles by coating the inert base particles with a first mixture including at least one algaecidal material comprising cuprous oxide, and a void-forming material, the void-forming material releasing gaseous material at temperatures above 90 degrees C., and having an average particle size no larger than 2 mm, to form a first layer on the inert base particles; (c) forming second intermediate particles by coating the first intermediate particles with a second mixture including a binder and a coloring material and not including a void-forming material; and (d) heating the second intermediate particles to release the gaseous material and form pores in the first layer to produce the roofing granules 2.-14. (canceled)
 15. An algae-resistant roofing product produced by a process comprising producing algae-resistant roofing granules, and adhering the granules to a roofing product stock material, the algae-resistant roofing granules being produced by a process comprising: (a) providing inert base particles; (b) forming first intermediate particles by coating the inert base particles with a first mixture including; a binder; at least one algaecidal material, and a void-forming material, the void-forming material releasing gaseous material at temperatures above 90 degrees C., and having an average particle size no larger than 2 mm, to form a first layer on the inert base particles; (c) forming second intermediate particles by coating the first intermediate particles with a second mixture including a binder and a coloring material and not including a void-forming material to form a second coating having a thickness of from about 2 micrometers to about 25 micrometers; and (d) heating the second intermediate particles to release the gaseous material and form pores in the first layer to produce the roofing granules. 16.-28. (canceled)
 29. An algae-resistant roofing product produced by a process comprising producing algae-resistant roofing granules, and adhering the granules to a roofing product stock material, the algae-resistant roofing granules being produced by a process comprising: (a) providing inert base particles; (b) forming green granules by coating the inert base particles with a mixture including; at least one algaecidal material, and a void-forming material, the void-forming material releasing gaseous material at temperatures above 90° C., and having an average particle size no larger than 2 mm, at least one coloring material; and a heat curable binder; and (c) heating the green granules to release the gaseous material to form pores and cure the binder to produce the roofing granules.
 30. An algae-resistant roofing product produced by a process comprising producing algae-resistant roofing granules, and adhering the granules to a roofing product stock material, the algae-resistant roofing granules being produced by a process comprising: (a) providing inert base particles; (b) forming first intermediate particles by coating the inert base particles with a first mixture including at least one algaecidal material, and a void-forming material, the void-forming material releasing gaseous material at temperatures above 90° C., and having an average particle size no larger than 2 mm, to form a first layer on the inert base particles; (c) forming second intermediate particles by coating the first intermediate particles with a second mixture including a coloring material; and (d) heating the second intermediate particles to decompose the void-forming material and form pores in the first layer to produce the roofing granules.
 31. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the first mixture further includes a binder, the binder comprising an aluminosilicate material and an alkali metal silicate.
 32. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the second mixture further includes a binder, the binder comprising an aluminosilicate material and an alkali metal silicate.
 33. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the at least one algaecidal material is selected from the group consisting of copper compounds and zinc compounds.
 34. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the at least one algaecidal material comprises cuprous oxide.
 35. The algae-resistant roofing product of claim 34, wherein in the process for producing the algae-resistant roofing granules, the cuprous oxide comprises at least 2 percent of the algae resistant granules.
 36. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the at least one algaecidal material further comprises zinc oxide.
 37. The algae-resistant roofing product of claim 36, wherein in the process for producing the algae-resistant roofing granules, the zinc oxide comprise at least 0.1 percent by weight of the algae-resistant granules.
 38. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the void-forming material comprises a substance selected from the group comprising ground walnut shells, sugar, and carbon black.
 39. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the void-forming material comprises at least 0.1 percent by weight of the algae-resistant granules.
 40. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the coloring material is selected from the group comprising transition metal oxides.
 41. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the second intermediate particles are heated to a temperature of at least 500 degrees C.
 42. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the granules have a pore size in the range of about 0.1 to 20 micrometers.
 43. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the first intermediate layer has a thickness of about 30 micrometers.
 44. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the second intermediate layer has a thickness of about 5 micrometers.
 45. The algae-resistant roofing product of claim 30, wherein in the process for producing the algae-resistant roofing granules, the second mixture further includes at least one algaecidal material. 